1. Field of the Invention
This invention relates generally to an exhaust system for a two-cycle engine, and more particularly, to an exhaust system for a two-cycle engine having, in the order from the engine to the atmosphere or muffler, a first expansion chamber having a first divergent portion and a rear cone-shaped portion, and a second expansion chamber having a second divergent portion.
2. Description of the Prior Art
In the conventional exhaust system for a two-cycle engine, as shown in FIG. 1, there is provided an elongated exhaust pipe having an expanded chamber, designated by the reference numeral 4. Expansion chamber 4 includes a diffuser portion 2 and a rear-cone portion 3. The diffuser portion 2 is in pneumatic communication with an exhaust port 1 of the two-cycle engine 100 (not shown) at an inlet opening 8 thereof. Diffuser portion 2 provides a divergent wall which defines a progressively expanding exhaust gas flow passage, having a cross-section which increases as the exhaust gas moves away from exhaust port 1. The divergent wall of diffuser portion 2 creates a pressure drop or relative vacuum substantially adjacent the exhaust port 1, which acts to draw out the exhaust gases from the engine 100. The rear-cone portion 3 is positioned downstream of the diffuser portion 2, and provides a convergent wall which defines a progressively reducing exhaust gas flow passage, having a cross-section which decreases as the exhaust gas moves from the diffuser portion 2 to a tail pipe 5. The convergent wall of rear-cone portion 3 acts to reduce the amount of engine noise present at tail pipe 5, while at the same time, acts to increase the pressure of the exhaust gas as it moves toward tail pipe 5. Tail pipe 5 has an exhaust gas flow passage of a constant diameter. Tail pipe 5, in turn, is in pneumatic communication either with the atmosphere or with a muffler 6. Alternately, a small flat pipe 7 may be attached to the tail pipe 5, a shown in FIG. 2. However, in any prior art embodiment, in the situation where the exhaust gases are discharged from a plurality of cylinders through exhaust manifolds, which in turn are in pneumatic connection with a single exhaust pipe, the Kadenacy Effect in the diffuser portion 2 of the exhaust pipe is not adequately created. In addition, in the embodiments where the rear-cone portion is in pneumatic connection with the muffler, the internal pressure of the exhaust gases in the muffler is increased, which results in a lowering of the performance and efficiency of the two-cycle engine 100.